Various types of biometric systems are used more and more in order to provide an increased security for accessing an electronic device and at the same time keep the user convenience at an acceptable level. In particular fingerprint sensors have been successfully integrated in such devices, for example, thanks to their small form factor, high performance and user acceptance.
In a fingerprint sensor, a captured image is compared to one or more stored fingerprint templates in order to verify the identity of the user. In order to avoid performing matching on an image which is of low quality, where it is likely that no successful matching can be performed, a quality metric is assigned to the captured image before matching to determine if the specific image should proceed to the matching step.
However, some people may have difficulties in using the fingerprint sensor, due to having so-called “difficult fingers”. For example, the characteristics of the fingerprint may be of generally low quality, i.e. fingerprint image contains low level fingerprint data. Alternatively, the fingerprint pattern may be difficult to detect due to a temporarily moisturized or dried-out finger.
When the fingerprint sensor is unable to properly match the captured image of the fingerprint with the one or more stored fingerprint templates, the user of the electronic device is often directed to provide a personal pin code for e.g. unlocking the electronic device. This has the effect that the fingerprint sensor cannot be sufficiently used. This may reduce the overall quality feel of the fingerprint sensor.
Accordingly, it is desirable to improve the usability of the fingerprint sensor.